Bio-based polymer is considered as one of potentially renewable materials to reduce the consumption of petroleum resources. We report herein on the one-pot synthesis and development of unnatural-type bio-based polysaccharide, α-1,3-glucan. The synthesis can be achieved by in vitro enzymatic polymerization with GtfJ enzyme, one type of glucosyltransferase, cloned from Streptococcus salivarius ATCC 25975 utilizing sucrose, a renewable feedstock, as a glucose monomer source, via environmentally friendly one-pot water-based reaction. The structure of α-1,3-glucan is completely linear without branches with weight-average molecular weight (Mw) of 700 kDa. Furthermore, acetate and propionate esters of α-1,3-glucan were synthesized and characterized. Interestingly, α-1,3-glucan acetate showed a comparatively high melting temperature at 339 °C, higher than that of commercially available thermoplastics such as PET (265 °C) and Nylon 6 (220 °C). Thus, the discovery of crystalline α-1,3-glucan esters without branches with high thermal stability and melting temperature opens the gate for further researches in the application of thermoplastic materials.

Non-biodegradable microplastics have become a global problem. We propose a new enzyme-embedded biodegradable plastic that can be self-biodegraded anytime and anywhere. Proteinase K from Tritirachium album was embedded in poly­(l-lactic acid) (PLLA). The PLLA solution-cast film with embedded proteinase K showed weight loss of 78% after 96 h incubation. In addition, PLLA extruded films embedding immobilized proteinase K encapsulated in polyacrylamide were produced at 200 °C and embedded-enzyme degradation was monitored. Immobilized proteinase K embedded in the extruded film maintained its degradation activity and degraded the PLLA film from inside to make small holes and cavities, suggesting that immobilization is a powerful technique to prepare thermoforms with embedded enzymes. The rate of embedded-enzyme degradation was accelerated by dividing the film into smaller pieces, which can be regarded as a model experiment for biodegradation of microplastics. Various biodegradable plastics with specific embedded enzymes will contribute to solve global environmental problems.

P[(R)-2-hydroxybutyrate] [P((R)-2HB)] is an aliphatic polyester analogous to poly(lactic acid) (PLA). However, little has been known for its properties because of a high cost of commercially available chiral 2HB as a starting substance for chemical polymer synthesis. In this study, P[(R)-2HB] and P[(R)-2HB-co-(R)-lactate] [P((R)-2HB-co-(R)-LA)] with a new monomer combination were successfully synthesized in recombinant Escherichia coli LS5218 from less-expensive racemic 2HB using an R-specific polyester synthase. The cells expressing an engineered polyhydroxyalkanoate synthase from Pseudomonas sp. 61-3 and propionyl-CoA transferase from Megasphaera elsdenii were grown on LB medium containing 2HB and glucose in a shake flask and accumulated up to 17 wt % of P[(R)-2HB] with optical purity of >99.1%. In addition, the same cells cultured in a jar-fermentor produced P(86 mol % 2HB-co-LA) copolymer. Notably, the molecular weights (Mw) of P(2HB) (27000) and P(2HB-co-LA) (39000) were 2- and 3-fold higher than that of P(2HB) previously synthesized by chemical polycondensation. P(2HB) was processed into a transparent film by solvent-casting and it had flexible properties with elongation at break of 173%, which was contrast to the rigid PLA. Regarding mechanical properties, P(2HB-co-LA) was tougher but less stretchy than P(2HB). These results demonstrated that P(2HB) has useful properties and LA units in 2HB-based polymers can act as a controllable modulator of the material properties. In addition, P[(R)-2HB] was efficiently degraded by treatment of Novozym 42044 (lipase) but not Savinase 16L (protease), indicating that the degrading behavior of the polymer was similar to that of P[(R)-LA].

Blend films containing wild-type poly[(R)-3hydroxybutyrate]] (P(3HB)) and ultrahigh-molecular-weight P(3HB) (UHMW-P(3HB)) (compositions of 5/95 and 10/90 w/w) were prepared by solvent-casting and subsequent colddrawing. The thermal properties, crystallization behavior, mechanical properties, and highly ordered structure of the blend films were analyzed by differential scanning calorimetry, polarized optical microscopy, a tensile test, and wide-and small-angle X-ray diffraction measurements with synchrotron radiation. The maximum radial growth rate of spherulites and corresponding temperature were identical for films of different composition. However, the half-time of crystallization of the blend films was shorter than that of P(3HB) because UHMW-P(3HB) behaves as a nucleating agent. The tensile strength, Young's modulus, and elongation at break of a 5/95 blend film after cold-drawing to 12 times of the original length were 242 MPa, 1.50 GPa, and 88%, respectively, which are higher than those of an UHMW-P(3HB) cold-drawn film and similar to those of common plastic films as poly(ethylene terephthalate). The wide-angle X-ray diffraction results indicated that the cold-drawn films with high tensile strength contained both 2 1 helix (α-form) and planar zigzag (β-form) conformations. Addition of a small amount of UHMW-P(3HB) to P(3HB) caused the β-form to appear in blend films at a high drawing ratio. A mechanism for forming β-form crystals in the blend films is proposed. Enzymatic degradation of the cold-drawn blend films is demonstrated using polyhydroxybutyrate depolymerase, suggesting that the rate of enzymatic degradation can be controlled by addition of UHMW-P(3HB).

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Copper (titanium) [Cu(Ti)] films with low titanium (Ti) concentration were found to form thin Ti-rich barrier layers at the film/substrate interfaces after annealing, which is referred to as self-formation of the barrier layers. This Cu(Ti) alloy was one of the best candidates for interconnect materials used in next-generation ultra-large-scale integrated (ULSI) devices that require both very thin barrier layers and low-resistance interconnects. In the present paper, in order to investigate the influences of annealing ambient on resistivity and microstructure of the Cu alloys, the Cu(7.3at.%Ti) films were prepared on the SiO 2 substrates and annealed at 500°C in ultra-high vacuum (UHV) or argon (Ar) with a small amount of impurity oxygen. After annealing the film at 500°C in UHV, the resistivity was not reduced below 16 lW-cm. Intermetallic compounds of Cu 4 Ti were observed to form in the films and believed to cause the high resistivity. However, after subsequently annealing in Ar, these compounds were found to decompose to form surface TiO x and interfacial barrier layers, and the resistivity was reduced to 3.0 lW-cm. The present experiment suggested that oxygen reactive to titanium during annealing played an important role for both self-formation of the interfacial barrier layers and reduction of the interconnect resistivity.

In our previous studies, thin Ti-rich layers were found to uniformly cover SiO 2 /Si substrate surfaces at the interface with Cu(Ti) alloy films after annealing at elevated temperature. These Ti-rich layers were also found to prevent intermixing between the Cu(Ti) alloy films and the substrate, resulting in a simple barrier formation technique, called ''self-formation of the diffusion barrier,'' which is attractive for fabrication of ultra-large scale integrated (ULSI) interconnect structures. In the present study, to understand the mechanism of self-formation of the Ti-rich barrier layers on the substrate surface, the effects of SiO 2 /Si, SiN/SiO 2 /Si and NaCl substrate materials on the interfacial microstructure were investigated. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) interconnects. It was concluded that the chemical reaction of Ti with the substrate materials was essential for the self-formation of the Ti-rich layers.